Rheostats



Mare}! 1956 A. P. CHARBONNEAU RHEOSTATS 3 Sheets-Sheet l 'iled June 11., 1953 INVENTOR. ALLAN P. CHARBO/VAAU ATT RNE.Y

Marc}! 1956 A. P. CHARBONNEAU 3 Sheets-Sheet 2 Filed June 11, 1953 INVENOR. ALL /1/V P, CHABOA/A4I/ A. P. CHARBONNEAU Match 13, 1956 RHEOSTATS 3 Sheecs-Sheet 3 Filed June 11, 1955 .A/VENTO ALLA/V P, CHARBON/V540 United States Patent O RHEOSTAIS Allan l. Charbonneau, Wauwatosa, Wis., assimor t o Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application June 11, 1953, Serial No. 360,909

10 Claims. (Cl. 201-48) This invention relates to improvements in rheostats, particularly plate-like rheostats wherein the resistor assembly is embedded in insulating material within a fiat relatively thin housing.

One object of this invention is to provide such a rheo stat which has a minimum number of parts, is easy to assemble accurately, and is fully enclosed and protected.

Another object of this invention is to provide such a rheostt which has efiicient heat dissipation and consequent high rating and flexible application.

A further object is to provide a rheostat which may be regulated to eiect resistance variation in small increments or steps.

A still further object is to provide such a rheostat which is irOH-cIad to provide rapid dissipation of heat and bennetically sealed to prevent faulty operation due to the inclusion of moisture or other foreign materials.

The novel features, which are considered characteristic of the invention, are set forth With particularity in the appeuded claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Figure 1 is a view in side elevation of a first embodiment employing the invention, parts being broken away to expose the resistor assembly;

Fig. 2 is a view partly in end elevation and partly in section taken on the line 22 of Fig. 1;

Fig. 3 is an enlarged iragmentary sectional view taken on the line 33 of Fig. 1;

Fig. 4 is an enlarged fragmentary sectional view taken -onthe line 44 of Fig. 1;

Fig. 5 is a VieW in side elevation or the contact assembly with parts broken away; and

Fig. 6 is a view in side elevation of a second embodi ment employing the invention, parts being broken away to expose the resistor and terminal assemblies.

The rheostats shown in the drawings in general consist of a housing, including a resistor section and a contactor section, a resistor assembly positioned in such resistor section, a contact assembly associated with the resistor assembly, and a contactor assembly movably positioned in said contactor section and associated With the contact assembly. One of the features of this invention is the efficient dissipation of heat from the resistor assembly. This is accomplished by positioning such assembly in between the fiat metal walls of the resistor section, packed in a granular refractory powder having electrical insulation and good heat conduction.

The housing is made up of two substantially identically shaped saucer-like steel plates 10. While shown as circu- 1ar because such form is convenient to use, they can take other peripheral shapes. Each plate has a peripheral flange 12 placed in abutting position and welded together during assembly. Adjacent such flanges are offset annular shoulders 14 which grip and hold the resistor assembly. At suitably arranged places on the plates, the flanges and shoulders are provided with grooves 16 which cooperate to make seats for the terminals. An additional set of grooves 18 in such flanges and shoulders cooperate to form an opening for the insertion of the insulating powder. The fiat relatively closely spaced walls of the plates 10 form the resistor section of the housing, such walls providing a large area for radiation of heat. The central part of the plates 10 have laterally projecting cylindrical flanges 20 which define the contactor section of the housing. For the purposes hereinafter described, one of the plates 10 has a pair of posts 22 (see Fig. 4) and the other plate a pair of female elements 24 constituting a compression lock. To suspend the rheostat for usage there are several angularly spaced mounting blocks 26 welded to the. flanges 12 as shown.

In the first embodiment shown in Fi 1 are two resistor assemblies which fit entirely within the resistor section of the housing. Only one of such assemblies will be described in detail. It consists of a resistor plate 28 which is in the form of a segment of a circle extending approximately It is made of insulating material. its outer arcuate edge has notches 30 spaced angularly 2 /2 Notches 30 are sufiiciently deep so that when the formed resistance is seated at the bottoms thereof there will romain a suflciently large outer margin of plate 28 to be properly held by the offset shoulders 14 and to provide electrical clearance between the resistance and said shoulders. The inner arcuate edge of the resistor plate 28 has notches 32 arranged in pairs. The notches of a pair are angularly spaced at 2 /2 and there are 5' between each pair. The resistance element is made up from units of formed resistances 34, each of which has 5 spaced bights between the ends thereof. The longer end is attached to a contact by welding or silver soldering and the shorter end is wrapped around the long end of an adjacent unit. Each unit occupies one of the pairs of notches 32 and three of the notches 30. The righthand end of one resistor assembly and the lett-hand end of the other resistor assembly (Fig. 1) are each connected to an exterior terminal 36 by a lead wire 38. Each terminal 36 (sec Fig. 3) comprises a metal tube 40 welded in place as shown and a threaded end 42 to which the external circuit Wiring is attached. Sait! threaded end 42 is attached to a conducting rod 46 as by means of welding. Said rod 46 is centrally disposed Within said tube 40 and is surrounded by insulating material 48. Positioned on said conducting rod 46 and held in a compressed state between said end 42 and said tube 40 are mica insulating washers 44.

The contact assembly and its method of manufacture are essential features of this invention. The contact assembiy includes two contact rings or spiders cf identical construction. Each ring is blanked from a sheet et hard temper silver or other suitable sheet eiectrically conductive material and after being blanked (see Fig. 5) has an enter ring 50 shown in broken limes from which necks 52 inwardly project and terminate in wide contacts 54. Each contact has a hole 56 into which the base material is moided to anchor the contact. Tne contacts 54 are spaced 15. In olanking the spider, an inner ring 58 (only part of which is shown in the shaded area) WiLll fingers extending between the contacts 54 is first cut from the blank and is then pushed back into flush position. The purpose or ring 58 and its associated fingers is to form part of the mold and to hold the contacts 54 properly spaced during molding. In molding the assembly, the two contact rings are held in parallel spaced relationship by the outer rings 50. The rings are offset angularly so that the contacts of one ring are in line with the spaces be- 3 tween the contacts of the other ring. While so held the central parts of the contacts are embedded in a molded cylindrical base 643 and the contacts 54 rest flush against an inner web 62. The matefial for such molded base and web is preferably a glass filled silicone. After the material is set the outer rings 50 are severed from the necks 52 as indicated by the broken line and the inner rings 58 With their fingers are removed. This eliminates all connection between the contacts 54 and they become electrically independent. In the molding of the base 60, insert mots 64 are positioned as shown to provide securing means for a support ring and cover. The contactor assembly is now connected to the resistor assembly by Welding or silversoldering the ends of the formed resistances 34 to the nccks 52 as shown.

The resistor assembly and contact assembly as assembled and including the terminals 36 connected thereto are then seated in one of plates 10 with the outer periphcries of the resistor plates 28 resting on the shoulders M and the base 60 fitted in the cylindrical flange 20. The other plate 10 is then placed on the first plate to clamp the resistor plates 28 between the annular shoulders 14 and the terminals 36 in the grooves 16. "Ihe flanges 12 and tubes 40 are then Welded to complete the structure. The outer wall of the molded base 60 co operates with the plates 10 to form the resistor section and tohold the resistor assembly located therein. This section is then filled through the opening formed by the grooves 18 with an insulating powder 65 (sec Fig. 4) which has the dual characteristic of being a good electrical insulator and a good heat conductor. Magnesium oxide in powdered form may be used for this purpose. When such section is filled With the powder, the walls of the unit are squeezed in a press With a force to compact and compress the magnesium oxide, thereby elimi nating air spaces and increasing the thermal-conductivity of the powder. Such pressure also effects a press fit between the outer periphery et base 60 and the cylindrical fiange 20 to thus provide a hermetic seal therebetween. While the unit is held in the press, the ends of the posts 22 are riveted over to keep the walls from separating When the pressure is released. When the completed rheostat is put to use, the heat generated in the resistance element will be quickly conducted through the compacted magnesium oxide powder to the relatively large area of metal on both sides and will be eflciently dissipated by radiation.

The contactor assembly has a hub 66 molded from insulating material and formed With external notches 68 and 68 and a centrally located Dshaped opening 70. Two metal contact levers 72 are shaped as shown to fit on the hub 66 and to engage notches 68 and 68 to prevent relative rotation therebetween. Contact levers 72 are formed With surfaces 74 which slide along the contacts 54. Said contact surfaces 74 are placed at opposite ends of a diameter; one of said surfaces being displaced from said diameter by one-quarter of the angular distance betWeen adjacent contacts. This angular relationship assures that only one of the contact surfaces 74 will be moved from one to another of adjacent contacts at a given time. The contact levers 72 are conneted by a flexible connector 76. To install the contactor assembly one contact lever is first inserted longitudinally through the opening in web 62. The connecter 76 is made long enough for such purpose. The contact levers are then arranged in juxtaposition With the contact surfaces 74 alined and resting on their respective series et contacts 54. While so held the hub 66 is inserted through the openings in such levers and compression springs 78 slipped over each and of the hub. The springs 78 are compressed by glands 80 which fit over the ends of the hubs and are held in place by snap rings 82. The contactor assembly is now in place and may be rotated withrespect to the contact assembly. However, there will be s0me radial freedom until an operating shaft is inserted in the opening 70 of the hub. The c0ntactor section of the housing is enclosed on one side by a glass disk 84 which is held in place on a gasket 86 on the base 60 by a support ring 88 held by screws threaded in the insert nuts 64. The glass disk 84 permits the rheostat operator to use the arms of contact lever 72 as indicators to provide visual determination of the amount of resistance inserted in the circuit. The other side of the contacter section is covered by a fiat insulating plate 92 formed With a central opening 94 for accommodating an operating shaft. Such plate 92 is held on a gasket 96 on base 69 by screws 90.

The rheostat may be regulated from maximum resistance to minimum resistance by rotating the contacter by a shaft (mot shown) extending into the opening 70 through the opening 94.

Fig. 6 shows a second embodiment of my invention wherein like components are used as described above With respect to the first embodiment. Said Fig. 6 shows the use of a single resistor assembly in the form of a segment et a circle extending approximately 300. The resistor plate 1% is formed With notches 39 spaced angularly along its outer periphery and With pairs of notches 32 along its inner periphery, as explained above With regard to the first embodiment.

Fig. 6 shows the contact assembly of the second embodiment as being the same as the contact assembly for the first embodiment except for the metal contact levers 102 and slip rings ll4. Similar to the first embodiment, there is provided in the device of Fig. 6, a pair of contact levers 162 axially alined and non-rotatably attached to hub 66. As aboveexplained With regard to Fig. 5, contacts 54 are staggered on opposite sides of the inner web 62 to provide a maximum number of resistance steps. A contact 54 on each side of inner web 62, is formed With a slip ring 04 to permit continued engagement of ring 1M with the contact lever 102 during rotation of the latter. Contact levers 102 are each formed With a contact surface 74 for engagement With contacts 54 and with a contact surface 106 for continued engagement With slip ring 104. As is beleved readily apparent to persons skilled in the art, contact levers 102 can be formed from contact levers 72 by removing a portion of the ends thereof and by providing a contact surface 166 for engagement With ring 104.

Terminals 36 are placed as shown in Fig. 6 and are attached to nebks 52 of contacts 54 to provide electrical continuity from either of the outside terminals 36 through the resistances 34 to the other outside terminal.

As will be apparent to those persons skilled in the art, the device shown in Fig. 6 can be used as a variable resistance unit by connecting themiddle terminal and one of the outer terminals together. Further, such device may be used as a potentiometer by individually connecting each of the three terminals 36 to the proper cir cuit connections.

The methods for making the several sub-assembles, and the method of making the complete rheostat are identical With or very similar to the methods heretofore described With regard to the first embodiment. In view of such similarity reference should be had to the method of making the first embodiment, if it is desired to construct the device of Fig. 6.

Although only one embodiment of the invention is shown and described herein, it will be understood that this application is intended to cover such changes or modifications as come within the spirit of the invention or scope of the following claims.

I claim:

1. in a rheostat of the character described, a resistor assembly comprising a segmentally shaped insulating resistor plate, a plurality of notches extending substanfially inwardly of the outer arcuate edge of said plate, a plurality of notches on the inner arcuate edge of said plate, and a plurality of preformed resistance nuits carried in said notches, each unit having an inwardly projecting lead adapted to be connected with a contact, said leads being also connected With ad,iacent un1ts.

2. In a rheostat of the character described, a contact assembly comprising a base of insulating materia] having a central bore, a pair of axially spaced superimposed rings et contacts carried by said base, each of said rings having a plurality of equally angularly spaced contacts extending radially inwardly toward said bore, said contacts having terminal ends extending radially outwardly o-f said base, said rings of contacts being angularly offset whcrcby tire contacts or one ring are alined With the spaces betwecn the contacts of the other ring.

3. In a rheostat as clairned in claim 2, a pair of juxtapositioned contact levers m-ounted within said bore, one of said contact levers having contact surfaces in wiping engagement With the contacts of one of said rirgs, the other of said contact levers having contact surfaces in Wiping engagement With the contacts et the other or said rings, and means electrically interconnecting said contact levers.

4-. The contact levers as claimed in claim 3 in which the contact surfaces on each contact lever are angularly spaced to afi'ord transfer of only one of said contact surfaces from one contact to another at a given time.

5. in a rheostat as claimed in claim 3 a pair of springs and spring glands for resiliently holding said contact levers in wiping engagement with said contacts.

6. In a rheostat of the character describcd, a contact assembly comprising a base et insulating material having a central bore, a pair et axially spaced superimposed rings of: contacts carried by said base, each of said rings of contacts having a plurality 0J equally angularly spaced contacts cxtending radially imvardly toward said bore and a slip ring electrically connected to One et said contacts, said contacts having terminal ends extending radially outwardly of said base, said rings of contacts being angularly offset Whereby the contacts of one ring or contacts are alined With the spaces between the contacts of the other ring of contacts.

7. In a rheostat as claimed in claim 6 a pair of spaced contact levers monnted within said bore, each of said contact levers having a first contact surface in Wiping engagement with the contacts of one of said rings et contacts and a second contact surface in wiping engagement With the slip ring of said one of said rings et con tacts, and means electrically interconnecting said contact levers.

8. In a rheostat as claimed in claim 7 a pair of springs and spring glands for resiliently holding said contact levers in wiping engagement with said contacts.

9'. A rheostat comprising a resistor plate, a resistor carried by said resistor plate, a plurality 0f contacts conneeted with said resistor at spaced intervals, a contactor movablc rclativeiy to said contacts for selective engagement therewith, a metal casing for said rheostat having spaced opposed walls fcrming a section for housing said resistor, said Walls providing areas on both sides of said resistor cr dissipating heat and having outer marginal offset shoulders ccoperating to engage said resistor plate and form a support therefor, and heat conducting and electrical insulating material Within said section and surrounding said resistor, said wall having centrally located cylind;.cal anges defining a section for housing said contacter Within which is supported et contact holding base of insulating material, said base cooperating With said walls to define said section for housing said resistor and said resistor plate, and in which said Walls have a locking element therebetween which is secured while said walls are pressed toward one another [o compress said insulating material.

10. A rheostat comprising a resistor plate, a resistor carried by said resistor plate, a plurality cf contacts connected With said resistor at spaced intervals, a contactc-r movable relativey to said contacts for selective engagement thcre.vith, a metal casing for said rheostat having spaced opposed walls forming a section for housing said resistor, said walls providing areas on both sides c-f said resistor for dissipating heat and having outer marginal offset shoolders cooperating to engage said resistor plate and form a support theretor, and heat conducting and electrical insulating material Within said section and surrounding said resistor, and said walls having a locking element therebetween which is secured while said walls are pressed toward one another to compress said insulating material.

References Cited in the file of this patent UNITED STATES PATENTS 1,993,410 Lightfoot Mar. 5, 1935 2,127,083 Howe Aug. 16, 1938 2,606,985 De Bell Aug. 12, 1952 FOREEGN PATENTS 558,735 Great Britain Jan. 18, 1944 658,395 Great Britain Oct. 10, 1951 

